Telecommunications networks such as third generation partnership, 3GPP, networks provide functions that implement online charging. Online charging is a process where charging information for network resource usage is collected concurrently with that resource usage. However, authorization for the network resource usage must be obtained by the network prior to the actual resource usage to occur. This authorization is granted by the Online Charging Server, OCS, upon request from the network. More specifically, a subscriber account located in the 3GPP OCS is queried prior to granting permission to use the requested network resource(s). In other words, online charging is a mechanism where charging information can affect, in real-time, the service rendered to the user/subscriber.
3GPP has standardized an OCS specified in 3GPP technical specification TS 32.296. FIG. 1 (Prior art) illustrates a simplified architecture of the 3GPP OCS providing online charging for services provided by the Evolved Packet System, EPS, as specified in 3GPP TS 23.203 and 3GPP 23.401.
The network entities, NE, of the EPS such as the packet data gateway, PGW, illustrated in FIG. 1 (prior art) and optionally the policy control and charging function, PCRF, furnish charging information to the OCS in order to perform Credit-Control before the network resource usage is permitted. To support online charging for services provided to a subscriber, a prepaid subscriber account has to exist in the OCS, against which the resource usage in the EPS can be billed. Hence all activities to assess the requested resource usage, to determine its value in monetary or other units, and to debit these units from the subscriber account, must occur prior to or at least, during the resource usage, i.e. online with respect to resource usage. Depending on the circumstances, a final evaluation must occur when resource usage ends. Two cases of performing online charging are described:                Direct Debiting: the requested resource can be determined and billed in a one-off procedure. In that case, the resource usage is debited from the subscriber account immediately when processing the charging event, and the permission for the resource usage is returned to the network. An example of this may be the forwarding of a terminating short message. In this scenario, it is generally required that the network can guarantee resource usage execution in order to avoid over-billing the user.        Unit Reservation: the OCS cannot a priori know the amount of resources that the end user may eventually consume, or it cannot be assumed a priori that the resource usage request can be (completely) fulfilled. In this case, a certain amount of (monetary or non-monetary) units is blocked, or reserved, on the subscriber's account on the OCS, and permission to use an amount of resources that matches the unit reservation is returned to the network. When the granted units have been used or a new, not yet authorized chargeable event occurs, the network must send a new request for unit allocation to the OCS. When resource usage has been executed, the actual amount of resource usage (i.e. the used units) must be returned by the NE to the OCS so that eventually over-reserved amounts can be re-credited to the subscriber account, assuring that the correct amount gets debited.        
In present OCS, the amount to be reserved by Online Charging System (OCS) is more or less fixed/pre-configured depending upon for example the rating and services are either denied or granted or interrupted if the subscriber account is depleted.